Metallic vessels or containers are usually made by firmly connecting or joining a bottomed lower piece (main part of the container) of cylindrical form and an upper piece (lid part so to speak), with a mouth portion on top, of inverted bowl form downwardly open, at the abutting portion of the two. Those metallic vessels (containers) may be utilized in various purposes, and the most serious problem therein has been the heavy weight which they can hardly evade because of the metallic material. As a naturally thought countermeasure, a metal plate or slab of small thickness has been tried, but the thinner the metal plate becomes, the more often the pressure-resisting capacity of the container appears as a problem. Sometimes a deformation or buckling of the container happens during its actual use. In some other instances a too thin metal plate makes the formation of the lower piece or the upper piece itself very difficult, i.e., provides a problem of forming method.
On the other hand, vessels or containers made of aluminum or its alloys are widely used because of their strong points in light weight and corrosion resistance. Their good features, in being harmless to the contained matter because of the corrosion resistance and in being flexible in formation, allow them to be broadly utilized for containing foods or the like. When such a container of aluminum (or aluminum alloy) is utilized for beer container, it is required to be inner-pressure resistant in the order of 3-4 Kg/cm.sup.2 because of beer being a foaming beverage. So the container of aluminum (or aluminum alloy) must be, while being required to be as thin as possible in its wall thickness within the allowable extent for the purpose of weight decreasing, sufficiently inner-pressure resisting and suitable for formation as well. This is an inherent and difficult problem to be solved for the container of this type.
Such a container, when it is used as a beer container for example, must be provided with a mouth portion in its upper piece for filling or emptying the contained liquid. However it becomes a very difficult problem to integrally form the mouth portion there when the wall thickness of the container is diminished to a certain limit.